CN1283744C - Ice nucleating non-stick coating - Google Patents
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- CN1283744C CN1283744C CNB028133765A CN02813376A CN1283744C CN 1283744 C CN1283744 C CN 1283744C CN B028133765 A CNB028133765 A CN B028133765A CN 02813376 A CN02813376 A CN 02813376A CN 1283744 C CN1283744 C CN 1283744C
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Abstract
Heterogeneous surface with polar functional groups as nucleation points. These nucleation points cause precipitation of a substance, for example ice or salt, in a fluid at these nucleation points under suitable physical conditions because the Gibbs free energy of the system is lower at the nucleation points than between the nucleation points, where said system comprises said surface and said fluid with said substance near said surface.
Description
Technical Field
The present invention relates to ice non-stick surface coatings.
Background
The ice layer on industrial surfaces often causes serious safety hazards and damage in industrial applications. In winter ice formation, in particular on aircraft wings, ship decks and cables, is well known. Avoiding such ice formation and reducing the adhesion between ice and surfaces has therefore been the focus of international research and development for the last decades.
Hydrophobic surface properties are a well-known basis for designing ice repellent coatings. Over the last 30 years, a larger number of different coating systems have been developed and put into use. By definition of work of adhesion, materials such as ptfe (teflon) or polyethylene, which are primarily water repellent, have been chosen with very low surface tension. In recent years, new polysiloxane-containing coatings such as PDMS (polydimethylsiloxane) have also been introduced for this purpose.
For atmospheric ice, such problems can be partially solved by these coatings. However, the lifetime, the mechanical stability and also the stability of the release properties do not meet the expectations. Commercially available icephobic (icephobic) coatings generally inhibit freezing due to their hydrophobic effect. Unfortunately, in the case of certain undercooling, strong icing occurs on these coated surfaces, destroying the icephobicity. Challenges remain particularly for aircraft applications.
Ice making on cooled surfaces for refrigeration or ice cream production presents similar challenges: the ice required and formed here has to be removed by expensive mechanical scraping devices or by short-term heat input. The above coatings have also attempted to be applied in this regard, but without success. This is mainly due to the following three reasons: during use, the coating properties change, in particular due to wear; due to the very low thermal conductivity of these generally thicker coatings, the heat transfer is significantly reduced; and due to the low wetting power of these surfaces, the rate of icing is greatly reduced.
The crystallized ice adheres with strong adhesion to the cooled heat exchanger surfaces of normal handling. A flat compact ice layer will be produced, depending on the temperature gradient formed with the flowing brine only on the cooling surface. If not removed, for example by a mechanical scraping device, the ice layer may increase in thickness over time, causing the flow to decrease and eventually stop.
Existing developments based on fluorine-containing organic coatings do not overcome this problem. Typical water repellency properties of fluorinated organic surfaces at room temperature generally do not translate into ice repellency properties in practical applications.
Fluorine-containing coatings such as the commercial products PTFE, FEP have been tested, as have fluorinated alkoxysilanes from different sol-gel coating systems, but their icephobicity generally appears to be inconclusive. In these tests, the fluorochemical coatings exhibited the highest hydrophobicity at contact angles of about 95 to 115 degrees for water and water/freeze inhibitor solutions. But this higher hydrophobicity has no significant effect on the icing behaviour of the surface. Based on these experiments, it can be concluded that hydrophobic surfaces are not necessarily also icephobic. It is clear that the apparent hydrophobicity of the fluorine-containing coating system is no longer effective when ice crystals with strong polarity and directional dipole moment are formed on the surface. In highly electronegative fluorine, dipoles appear to be induced, resulting in the generation of secondary forces and ice adhesion. Furthermore, due to the well-known porosity of the sintered PTFE surface, mechanical interlocking of the ice crystals formed on the PTFE surface also occurs.
Although existing varnish coatings based on polysiloxanes exhibit good ice repellency, the very insufficient mechanical stability and the very low thermal conductivity of these coatings make them impractical for use. The more abrasive ice particles break down these coatings already formed in a short time. In addition, the greatly reduced ice nucleation rate is another highly negative factor.
According to the disclosure of international patent application WO 00/06958, sol-gel technology has been used to produce corrosion resistant hydrophobic coatings which also appear to prevent ice formation on the evaporator surface. However, this case is only effective for surface temperatures very close to the freezing point. If the temperature of the surface is significantly below freezing, ice will formon the surface, albeit in a hydrophobic condition.
Summary of The Invention
The object of the present invention was to develop a novel surface coating which has non-stick properties with respect to icing or other precipitated substances in the fluid.
This object is achieved by a heterogeneous surface having nucleation points for precipitation of a substance in a fluid at these nucleation points under suitable physical conditions, wherein the heterogeneous surface is arranged such that the Gibbs free energy at said nucleation points is lower than between said nucleation points when the surface is in contact with said liquid and said substance.
Suitable physical conditions refer to conditions under which precipitation can occur. For ice formation, the physical conditions are suitable temperatures, and for precipitation of salt from the liquid, the physical conditions also include the concentration of salt in the liquid.
A heterogeneous surface is a heterogeneous surface that contains at least two physically and chemically different components, e.g. regularly or statistically distributed, wherein one of the components may be, for example, a polar functional group.
For example, the nucleation sites are covalently bonded to the material constituting the heterogeneous surface, although this is not necessarily essential to the basic idea of the invention.
The nucleation sites are preferably reactive functional groups or residues. In a practical embodiment of the invention, the nucleation sites may be reactive hydrophilic functional end groups, such as epoxy, amino, carboxyl, hydroxyl, methacryl. However, polymers such as polyaniline may also be used to form nucleation sites.
Preferably the heterogeneous surface comprises at least one of:
-polar regions as nucleation points and non-polar islands between said nucleation points,
-hydrophilic areas as nucleation points and hydrophobic islets between said nucleation points,
fragments with high surface energy as nucleation sites, surrounded by a low surface energy matrix,
spaced reactive residues as nucleation sites, e.g. OH-Or O-Due to organically substituted alkanes
The crosslinking process between the functional end groups of the oxide results and is surrounded by a non-reactive functional matrix.
According to the invention, the polar groups can be distributed regularly or statistically over the surface area and can, for example, be crosslinked thermally with the component surface and/or with metal alkoxides and/or with organic polymers, which are then crosslinked with the component surface. These polar functional groups are surrounded by non-polar compounds and are surface cross-linked to the component in a similar manner, isolating and separating the polar segments from each other. In particular, the reactive functional groups can be crosslinked with hydrophobic organic polymers to achieve larger regions with ice repelling hydrophobic properties and smaller local regions with hydrophilic properties as nucleation sites.
In fact, from polymeric molecular polysiloxane alkoxylates Si (OR)4Organo-modified polysiloxane alkoxylates (R-Si (OR))3) And other organic polymers through hydrolysis, condensation and addition reactions to produce hybrid layers forming inorganic-organic networks.
In a first step, nanoscale particles of the coating are synthesized by sol-gel techniques, which involve the synthesis of functionalized nanoscale particles from functionalized silanes:
as organic reactive end groups, aryl and alkyl residues are used.
These nanoparticles are crosslinked with an alumina layer on a solid surface, such as the surface of a tubular or plate heat exchanger. In addition, these particles may additionally be crosslinked with hydrophobic polymers to further increase release properties and ice repellent surface area. For the present invention, alkylbenzenes and alkylphenols are used.
Due to the choice of reactive end groups of the organosilane, the smooth nanostructure layer contains both hydrophobic anti-adhesive compounds and hydrophilic segments. To obtain these hydrophilic segments, polysiloxane alkoxylates or other organic components such as polyaniline with reactive hydrophilic functional end groups such as epoxy, amino, carboxyl, hydroxyl or methacryl groups are used. Due to this crosslinking process, it is possible to obtain isolated free polar groups or polar functional groups in the coating surface. In this way, very few hydrophilic segments are available to act as locally spaced nucleation sites.
The versatility of this approach allows a wide range of surface properties, since the features are the synthesis of hydrophilic as well as hydrophobic nanoscale particles and the choice of bridging organic fragments of different lengths.
The ice repellant coating developed herein is characterized by a smooth release surface having regularly spaced localized ice nucleation sites. Similar to chess games with black and white areas, smaller localized ice nucleation segments or sites with higher surface energy are surrounded by anti-adhesive anti-bornyl segments or regions with lower surface energy. These fragments exhibit hydrophilic and hydrophobic properties, respectively. Due to the locally different surface energy, the generation of a compact ice layer is significantly altered and avoided. Furthermore, the adhesion of the generated ice crystals is significantly reduced in strength and contact area. Thus, the removal of the generated ice crystals is possible only with brine flow along the surface. In view of these facts, it is possible to manufacture an ice maker without a moving scraping means.
Furthermore, the selection of the distance between the individual hydrophilic ice nucleation sites determines the size of the ice particles produced, which can be useful in processes where it is desirable or necessary to produce ice particles having a controlled size.
The thickness of the coating used is generally less than 10 microns. Therefore, the thermal conductivity thereof is greatly increased as compared with the conventional coating. Due to the formation of inorganic-organic networks which are covalently cross-linked to the metal or polymer surface, very good mechanically stable and abrasion resistant ice repellent surfaces are obtained. In addition, due to the covalent bonding, no coating delamination occurs.
As has been demonstrated in extensive studies on this problem and in various experiments, the underlying idea underlying the present invention is not limited to hydrophilic nucleation sites in a hydrophobic matrix. According to the present invention, local precipitation of species can be achieved if locally spaced polar nucleation sites with lower Gibbs free energy are present in the non-polar matrix.
The present invention is suitable for various applications, such as:
-producing ice crystals in air,
-producing ice crystals in a liquid,
-producing ice crystals in water containing a freezing point depressant,
-producing ice crystals in water containing ethanol,
-producing ice crystals in water containing propylene glycol,
-producing ice crystals in water containing ethylene glycol,
-producing partially melted crushed ice,
-producing an ice repellent surface of the component,
-a refrigeration system for cooling the refrigerant,
-an air-conditioning system for conditioning air,
-producing an ice-cream, the ice-cream,
-avoiding the adhesion of ice on the surface of the components,
to avoid ice sticking on aircraft, helicopter wings or wind turbine blades or ships,
-avoiding the adhesion of limestone on the surface of the components,
-precipitation of the salt in the liquid,
-precipitation of calcium carbonate in a liquid,
-precipitation of magnesium carbonate in a liquid, and
-precipitation of sugars in a liquid.
Brief Description of Drawings
The invention will be described in more detail with reference to the accompanying drawings, in which:
FIG. 1 is a representative schematic of the arrangement of INPs on the cell membrane of INA bacteria, wherein hydrophilic residues act as nucleation sites, which match the ice-like structure, and wherein adjacent hydrophobic residues are located around the nucleation sites to prevent ice from adhering to the cell membrane;
FIG. 2 shows an experimental set-up;
FIG. 3 shows a surface modification process of alumina by sol-gel technique using hydrophilic and hydrophobic residues;
FIG. 4 is a schematic illustration of the process of icing on cooled polar surfaces under flow conditions;
FIG. 5 illustrates different coating conditions, an
FIG. 6 shows a schematic view of the icing process on different coating materials; the images were taken once per second for a selected area of 7.7 x 5.8mm on the surface; the circles define nucleation sites and the arrows indicate the course of the crystals.
Detailed description/illustration of the preferred embodiments
The present invention can be understood with reference to the natural phenomena, as described below.
Natural phenomenon
It is known that living organisms in arctic and alpine regions have devised different countermeasures to survive in extremely cold conditions. Some of these organisms can reduce the freezing rate by nucleating ice at the earlier "warm" sub-zero temperature. Thus, the cells can release water and contract, counteracting osmotic pressure and avoiding freezing of the intracellular space. This activity has been reported in bacteria to insects and invertebratesIn the animal's organism. These organisms live in conditions with a high percentage of ice in their extracellular space and body fluids, but they maintain basal metabolism. They are called INA (Ice nucleation Activity) -organisms because they have a specific strain INA+To encode Ice Nucleation Protein (INP). INA-bacterial INP has been well characterized. They have a common repeat sequence of 8 amino acids, and they are located at specific sites on the cell membrane. As shown in fig. 1, Ice Nucleation Protein (INP)101 located on phospholipid membrane 102 constitutes a large complex from monomers with nucleation sites that are hydrophilic residues 103 surrounded by hydrophobic residues 104. These different physicochemical properties are obtained only by the modified tertiary and quaternary structure of INP. The position of the hydrophilic residues 103 appears similar to the ice structure, thus supporting the interaction of supercooled water molecules 105 with these nucleation sites 103. Due to the surrounding hydrophobic residues 104, the adhesion of ice 106 on the surface of the membrane 102 is minimized and ice crystals of certain sizes will be released.
INA-bacteria have been used as inducers of ice nucleation for different commercial purposes. One of the most studied INA-bacteria is the Pseudomonas syringae Populus alba (Pseudomonas syringae), the industrial application of which is the snowmaking patent system SNOWMAXTM。
The motivation for this work was to mimic the natural solution, i.e. mimic the mechanism of INA-organisms, to design a surface that can nucleate and release ice under flow conditions. Catalytically controlled local ice nucleation begins at an earlier sub-zero temperature. Due to the consumption of cooling energy in the interface/fluid, strong surface icing known from industrial coating systems can be avoided.
To mimic the biological cell membrane of INA-bacteria, sol-gel techniques have been used. It is known that INA-organisms require less than 60 units of INP to produce active nuclei at-5 ℃. This corresponds to about 1200 residues (150 kDa). Based on this knowledge, it is expected that the appropriate size of the reactive groups of the Ice Nucleation Coating (INC) is only a few nanometers.
To synthesize an INA-membrane like structure, a blend of nanoscale particles of different organosiloxanes was used to achieve a heterogeneous surface containing small spaced hydrophilic spots in a hydrophobic matrix. These hybrid coatings are transparent and have a thickness of 1-10 microns, depending on the type of INC. One big advantage of practical application is the low price of INC in mass production. This experiment will be described below.
Experimental device
The experimental setup shown in fig. 2 consists of a cooling system 201 and two interconnected circuits. The primary loop 202 is an industrial cryostat unit 204 operated with a 30% ethylene glycol/water mixture. The secondary circuit 203 comprises a 2.5 litre storage tank 205, a Grundfos CD050MF model pump 206 and a specially developed crystallisation chamber 207 which allows in situ observation of the ice crystallisation process.
The crystallization chamber 207 is designed as a heat exchanger. In the three channels 208, exchangeable half-tubes are mounted, covered on top with transparent windows to allow the process to be observed. The half-tube is 450mm long and 34mm in internal diameter. The total surface area of each half-tube was 480cm2. The chamber 207 is cooled from below. The entire system is insulated. Thermometers and flow meters are included in the present system. The temperature in the primary loop 202, the storage tank 205, and directly on the surface of the half pipe are measured. The thermocouples on the tube surface can be moved up and down in the cross section in the direction of the fluid to obtain a temperature gradient between the heat exchanger surface and the brine body. The rate of brine flow through the secondary loop may vary up to 0.7 liters/second.
Leica MZ12 with polarizing filter suitable for 3CCD SONY DXC 950P color camera5An optical microscope 209 is disposed above the upper window of the chamber. A videosequence is recorded during the freeze using a Pinnacle microvdeo DC 30plus computer camera system functionally connected to the computer system 210. A light-providing unit Schott KL 2500 LCD with polarizers operating at 3000K was included in the present device.
Experimental procedures
A mixture of demineralized water and a freeze-inhibitor was used in the experiment. Freezing point depressant additives are ethanol, propylene glycol and ethylene glycol. The concentrations of these additives were adjusted so that the mixtures reached freezing points of-2.5 deg.C, -5 deg.C and-7.5 deg.C, but only tested at-5 deg.C and-7.5 deg.C for ethanol.
To evaluate the icing capacity of the coating system, three tubes coated in the same manner were tested. Each crystallization experiment was repeated at least 3 times for each brine concentration. Depending on the results of these experiments, either further experiments were performed or the experiments were terminated. For each experiment, several video sequences of 90 seconds in length were taken during the ice crystallization.
The effect of parameters such as subcooling rate, flow rate and temperature gradient between the primary loop 202 and the secondary loop 203 on the crystallization behavior of the desired coating was tested to determine the appropriate method of producing ice crystals.
The amount of ice formed on the cooling surface is then estimated by means of image processing of the video sequence. Video and Image analysis was performed by using Adobe Premiere and Image-Pro Plus software. Within a selected time of 30 seconds, high quality pictures are taken from the video sequence per second. Black and white control analysis using Image-ProPlus software identified ice crystals and determined the average area. For a representative area of 7.7mm x 5.8mm, the values obtained are given as area percent of the total surface.
Raw materials
The exchangeable half-tube of the crystallization chamber is mainly manufactured from the aluminium alloy EN AW 6060. For some coating experiments, St52 steel half-pipes were also used. For most pipes, no other mechanical pre-treatments such as grinding, polishing or sandblasting are necessary prior to the coating process. To clean the tube surface, degreasing and etching are performed. For selected experiments, the tube surface was sand blasted with glass to increase surface roughness.
Various coatings were selected to find a surface treatment/modification that both nucleates and releases the ice formed. This option is based on reported coating systems found in the literature for ice repellency purposes. It includes organic coatings such as different types of PTFE systems and inorganic coatings such as nickel. The parameters that were varied in the experiments were surface energy, surface roughness, surface texture and coating thickness. Based on these experiences, new Ice Nucleation Coatings (INC) have been developed and evaluated in the crystallization chamber.
To produce the Ice Nucleation Coating (INC), a sol-gel technique is used, which is illustrated in fig. 3, which shows a surface modification 307 of the hydrolyzed aluminum oxide layer 301 on the aluminum 302. Nanoscale particles having hydrophilic 303 and hydrophobic 304 properties are synthesized from organically modified polysiloxane alkoxylates. These nanoscale particles 303, 304 are thermally crosslinked with the pretreated surface of the aluminum 302 half-tube via oxygen bridges 305. On the metal surface, a smooth and very thin nanostructured hybrid layer 306 is created, which is formed by an organic-inorganic network. The symbol Me in FIG. 3 is used to denote a metal atom, for example Al, Ti, Zr or Hf, or a semiconductor suchas Si. Due to the choice of reactive functional groups of the organosilane, the nanostructure layer contains both hydrophobic 304 anti-adhesive compounds and hydrophilic 303 segments. These very small hydrophilic 303 segments are believed to act as locally spaced nucleation sites. As is known from INA biology and as is for example the case in principle with a checkerboard with black and white areas, local ice nucleation sites are surrounded by anti-adhesive norbornyl segments or areas.
Results and discussion
As illustrated in fig. 4, under flow conditions, ice formation on the cooled surface 401 typically begins in the form of locally isolated heterogeneous nucleation. This process often occurs at non-homogenous points 402 on the surface 401, such as defects. The number of nucleation sites depends greatly on the surface structure and properties. This nucleation is followed by the growth 403 of nuclei larger than the critical dimension, resulting in a fusion 405 of these crystals. A thin and compact ice layer 406 is formed, the thickness depending on the growth time.
We examined dendrite growth in all the experiments performed. Our experiments with commercially available water and/or ice repellent coatings show freezing point depression effects for most of these coatings. Higher undercooling is necessary to nucleate ice compared to non-coated metal surfaces. The more hydrophobic the coating, the higher the supercooling required. Furthermore, we note that the crystallization rate of these coatings is much lower. These observations are consistent with the nucleation rate equation, which follows the Arrhenius equation.
In heterogeneous nucleation, the contribution of foreign surfaces to Gibbs free energy is given by f:
ΔGhet＝fΔGhom
f＝1/4(2+cosθ)(1-cosθ)2
where θ is the contact angle between the surface and the liquid. According to this equation, a higher contact angle between the liquid phase and the surface will increase the Gibbs free energy, while decreasing the nucleation rate. According to this theory, an ideal ice repellent coating should therefore not be wettable by the liquid phase to avoid surface nucleation. In the best case, homogeneous nucleation should occur close to the cooling surface. Unfortunately, all coating systems exhibit small defects in the form of, for example, pores, impurities, foreign inclusions or contaminants. It is therefore virtually impossible to completely avoid wetting of surfaces in aqueous systems for long periods of time.
In this regard, important explanations must be given to understand the effectiveness of the present invention. The prior art coating 501 on the metal surface 502 may have defects, in other words, holes or pores 503 in the coating 501 shown in fig. 5 a. In this case, the polar metal surface 504 at the bottom of the hole 503 may act as a nucleation point. However, such nucleation sites are not encompassed by the present invention for the following reasons. As ice or salt deposits occur in these holes 503, the side walls 505 of the holes 503 are subjected to increased pressure, forcing the side walls 505 and a portion of the coating 501 surrounding the holes 503 away from the surface, as indicated by arrows 506. The hole 503 then increases in size and the surface area of the remaining coating 501 decreases. Thus, the prior art coating 501 has a very short life in such applications.
As shown in fig. 5b and 5c, nucleation sites may also be formed by inorganic inclusions 508, 511 in the coating 501, such as metal oxide or carbide particles, which are part of the surface of the coating 501, which form ice upon contact with water. These particles are added to the coating system 501 primarily to increase abrasion resistance, but may in principle also form locally spaced nucleation sites due to their higher surface energy and polarity. However, such nucleation sites are not encompassed by the present invention for the following reasons. As ice formation proceeds on these particles 508, 511, strong adhesion will occur and over time the adhesion between the particles 508, 511 and the coating 501 will be reduced, which occurs mainly at the position indicated by the arrow 509 in fig. 5b and 5 c. Thus, if large ice crystals are formed, the attached particles are removed from the coating 501 after a certain time due to the strong tensile stress of the ice crystals. A hole 503 will be created in the paint 501 to show a similar effect as described above. Thus, the prior art coating 501 has a short life in such applications.
In contrast to the present invention, referring to fig. 3 and 5, functional groups 303, 514 are covalently bonded portions of the surface and coating 301, 501, respectively, such that similar damage is unlikely to occur. In fact, the functional groups even prevent the coating 301, 501 from being damaged due to icing or salt precipitation in possible holes or pores 503 of the coating 501, since icing or salt precipitation preferably occurs at the nucleation points 303, 514 and not in the holes 503. The reason for this can be easily understood by taking salt precipitation as an example. Since salt precipitation occurs at the nucleation sites, the salt concentration near the surface is reduced so that salt precipitation does not occur in the holes of the coating.
Referring to the experiment, regardless of the hydrophobicity of the industrial coating system examined, we found that ice crystallization started at the local point of dendritic ice crystal formation. In the early stages of crystal growth, these ice crystals are removed by a liquid stream for some coatings. But as a result of further growth, the individual single crystals fuse together to form at least a thin and compact ice layer. This thin ice layer adhered clearly to the surface for all the industrial coatings tested, as observed for the non-coated surface. If this thin and compact layer of ice forms first, the ice-releasing properties of the coating system are no longer effective. The thickness of the compact ice layer is continuously increased, thereby reducing the channel diameter. All ice crystals found in the liquid stream in the later stages of surface crystallization are caused by fragmented dendritic needles in the growing ice layer. Thus, the icephobic effect of the tested industrial coatings according to our experiments consisted in a reduction of the crystallization temperature and the icing rate. A common risk for all these coatings is coverage by a tightly compacted thin layer of ice, thereby negating ice repellency.
For fluorine-containing coatings such as industrial products PTFE, FEP, but also fluorine-containing alkoxysilanes from different sol-gel coating systems, their ice phobicity is not convincing. Here we found a similar behaviour to the other tested industrial coatings. These coatings exhibit the highest hydrophobicity at contact angles of about 95 to 115 degrees for water and water/freeze inhibitor solutions. But this higher hydrophobicity has no significant effect on the icing behaviour of the surface. It is clear that the apparent hydrophobicity of the fluorine-containing coating system is no longer effective if ice crystals with strong polarity and directional dipolemoment form on the surface. In highly electronegative fluorine, dipoles appear to be induced, resulting in the generation of secondary forces and ice adhesion. Furthermore, due to the well-known porosity of the sintered PTFE surface, mechanical interlocking of the ice crystals formed on the PTFE surface also occurs.
Unlike industrial coating systems, our experiments show that the novel biomimetic Ice Nucleation Coating (INC) is able to properly nucleate ice and release small crystals (0.1-2mm) under flow conditions. Four different scenarios are illustrated in fig. 6a-6d, showing four series of photographs, each series having 5 sequential images at 1 second intervals as shown at the bottom of the figure. We found that there are two different mechanisms of icing for the INC tested. The first consists in local nucleation and local growth of ice at specific Nucleation Points (NPs). This phenomenon is illustrated in fig. 6 a-c.
In fig. 6a, the nucleation point is encircled and ice crystals are seen to form and grow at the nucleation point until removed by the flow of brine at the most recent stage of the sequence, as shown in the rightmost image. Ice crystals of a few millimeters are formed and at the maximum stage of ice production, ice covers up to 5% of the cooling surface area. In fig. 6b, the nucleation site is surrounded, wherein ice crystals are formed and released in very small sizes. The ice crystals, indicated by the arrows in the image, are elongated as they flow with the brine. We call this mechanism the "snowball" effect. This mechanism indicates a significant improvement in efficiency in ice production. The ice crystals cover up to 10% of the cooling surface area.
The same situation is shown in the sequence of photographs of fig. 6 c. Not only one particle is formed, but a set of ice crystals is also formed. This multiple local ice nucleation can be achieved by increasing the number of hydrophilic nanoscale particles or reactive residues in the coating. This appears to increase ice production and the results show ice formation on up to 40% of the cooling surface area.
For a single Nucleation Point (NP), we note that nucleation is strongly dependent on flow rate. All tested INC's showed similar ice nucleation rates except for the coating shown in fig. 6 d. At an operating flow rate of 1.3m/s, the NPs generate ice crystals approximately every 5 seconds. As coating compositions and processing parameters were further improved, we attempted to increase the nucleation rate of NPs. The improved nucleation sites in the coating shown in fig. 6d clearly increased the ice nucleation rate, and some points were found to produce ice continuously. The working temperature and the blend composition have a slight effect on the results of the different coatings. All tested INC's appeared to operate significantly better when using aqueous propylene glycol solutions frozen at-5 ℃ or lower. Some of them also work well when used in less concentrated solutions frozen at-2.5 ℃.
The lifetime of the developed INC is an important factor for practical applications. The ice nucleation process and the ice crystals themselves hardly affect the surface stability of the coating. Thus, in addition to the icing method, the erosion resistance of INC is also a central task of our work. In several of the coatings tested, we found that the time-dependent aging process resulted in a reduced ability to release the formed ice. This effect becomes evident especially after a strong freezing of the surface due to very rapid supercooling. SEM analysis showed that some of the coatings used had defects and damage to the surface. We improved the coating properties of the developed INC by increasing the density of the inorganic network and selecting the functional groups of the other nanoscale particles. Furthermore, the content of inorganic compounds in the hybridnetwork is also varied to obtain the necessary mechanical and chemical stability of the coating. In addition, we anchor the organic bridged polymer in the coating network. Due to this, the performance of INC is significantly improved.
Conclusion of the experiment
It follows from experiments that it is possible to mimic the ice-making mechanism of INA-organisms. A technical approach to this mechanism with industrial applicability was developed using sol-gel technology. The design of the coating allows for improvements in the ability and effectiveness of ice production from local nucleation and growth of ice to process growth and increase in production of ice. The "snowball" effect was found to improve the quality of INC and appears to be the most effective way for a new ice maker. With multiple localized ice production of the coating shown in fig. 6c, up to 40% of the cooling surface area is free of ice adhesion. At a flow rate of 1.3m/s in this system, the NPs may generate ice crystals approximately every 5 seconds. This confirms that the principle can be used for continuous production of ice without ice adhesion.
Further applications
Generally, a large amount of ice making is required worldwide. It plays an important role in the food and refrigeration industry. In addition to ice cream production, direct contact cooling or freezing of food products and ice-slurry technology in industrial refrigeration and air conditioning are of high interest. In particular ice-slurries, which are mixtures of small ice particles, water and freeze inhibitors, are expected to be widely used in the future. Ice-slurry is considered a suitable alternative to common refrigerants such as CFCs and HFCs because it is an environmentally friendly coolant with high energy density capacity. In prior art industrial ice making machines, mechanical scraping devices remove ice formed on the cooling surfaces. They are not economically feasible due to the high cost in terms of design, energy consumption and after-sales service of mechanical scraping devices. Therefore, it is desirable to develop a new ice maker. With the surface coating according to the invention, scraping devices can be avoided. The flow of the ice-slurry constantly removes the generated ice particles from the nucleation sites of the cooling surface. Thus, a great step has been taken towards the practical implementation of ice-slurry in refrigeration and air conditioning systems using the surfaces of the present invention.
Although the principal aspect of the invention is the creation of an icephobic surface, for example for use in ice-slurry machines, the principles of the invention encompass a greater scope, as will become more apparent below.
Calcite is a stable form of calcium carbonate, the precipitation of which results in the well-known formation of limestone. The surface of calcite crystals is polar and bears a small negative charge. When the crystals are in contact with water, their surface is covered by a thin layer of water, in which the water molecules occupying the interface between the crystals and the water itself are also called the inner and outer Helmholtz layers. The water molecules have an ordered structure with a positive charge directed toward the crystal surface and bonded to the surface by secondary van der waals forces. In addition, in the interface, more precisely in the outer Helmholtz of the electrolytic double layer, positively charged calcium ions are also bonded. The initial interfacial interactions between calcite crystals and the second surface will occur through van der waals forces and hydrogen bonding across the ordered surface aqueous layer. The more polar the second surface, the stronger the interaction. In the hydrophobic apolar matrix of the invention, the structured surface with very small hydrophilic polar fragments involves punctate interactions with the interface, resulting in the local precipitation of calcite only at the nucleation sites. In the case of movement of the surrounding water, the formed calcite crystals precipitated at the nucleation points are removed from the nucleation points when the forces from the water flow-depending on the flow rate of the water and the crystals-are higher than the combination of calcite crystals precipitated at the very small nucleation points.
Further applications of the invention may be related to precipitation processes of salt or sugar in processing or in the food industry.
Claims (15)
1. A substrate having thereon a non-stick coating for nucleating ice, the coating having a heterogeneous surface with locally spaced polar segments as nucleation points for causing precipitation of species in a fluid only at the nucleation points and non-polar islands between the nucleation points, wherein the polar segments as nucleation points are covalently bonded to the species constituting the heterogeneous surface.
2. The substrate of claim 1, wherein the coating comprises an inorganic-organic network.
3. A substrate according to claim 1 or 2, wherein the coating on the substrate comprises hydrophilic segments as nucleation points and hydrophobic segments between said nucleation points.
4. A matrix according to claim 1 or 2, wherein the coating comprises fragments with high surface energy as nucleation sites, surrounded by a low surface energy matrix.
5. A substrate according to claim 1 or 2, wherein the nucleation sites comprise reactive functional groups or residues.
6. The substrate of claim 5 wherein the nucleation sites comprise reactive hydrophilic functional end groups or comprise polyaniline.
7. The matrix according to claim 6, wherein the functional end group is an epoxy, amino, carboxyl, hydroxyl or methacryl group.
8. A method of producing a non-stick coating for nucleating ice on a substrate, wherein the coating has nucleation sites which cause species in a fluid to precipitate only at the nucleation sites, the method comprising providing a substrate and providing a coating having a non-homogenous surface on the substrate, the operation comprising the steps of:
providing locally spaced polar segments as nucleation points,
covalently bonding the nucleation sites to the material constituting the heterogeneous surface, and
-providing non-polar islands between the nucleation points.
9. The method of claim 8, wherein the coating comprises a hybrid layer forming an inorganic-organic network comprising an organic polymer.
10. A method according to claim 8, wherein to obtain smaller hydrophilic fragments to act as locally spaced nucleation sites in the non-polar matrix, the method comprises
By organomodified polysiloxane alkoxylates R-Si (OR)3Synthesis of functionalized Nanoparticulate R-SiO with reactive end groups RxThis involves sol-gel techniques involving hydrolysis of R-Si (OR)3To obtain R-Si (OH)3And reacting R-Si (OH)3Condensation, wherein the reactive end group R comprises an aryl residue or an alkyl residue, to obtain hydrophobic particles;
providing organomodified polysiloxane alkoxylates Si (OR) having reactive hydrophilic end groups4Hydrophilic particles are obtained and blended with a sol having hydrophobic particles,
-thermally crosslinking the blended components on and with the surface of the substrate.
11. The method of claim 10, wherein the method comprises covalently bonding the segments through an oxygen bridge comprising a metal atom or a semiconductor, wherein the metal atom is Al, Ti, Zr, or Hf and the semiconductor is Si.
12. The process according to claim 10, wherein the silicone alkoxylate with reactive hydrophilic end groups is synthesized into hydrophilic nanoscale particles prior to blending, which involves sol-gel techniques.
13. The method according to claim 12, wherein the hydrophilic nanoscale particles contain a reactive group comprising an epoxy group, an amino group, a carboxyl group, a hydroxyl group, or a methacryloyl group, or polyaniline.
14. The method according to claim 12, wherein the hydrophilic nanoscale particles are crosslinked with a hydrophobic polymer, wherein the hydrophobic polymer is an alkylbenzene and an alkylphenol.
15. Use of a coating according to any one of claims 1 to 7 or produced according to the method of any one of claims 8 to 14 in at least one of:
-producing ice crystals in air,
-producing ice crystals in a liquid,
-producing ice crystals in water containing a freezing point depressant,
-producing ice crystals in water containing ethanol,
-producing ice crystals in water containing propylene glycol,
-producing ice crystals in water containing ethylene glycol,
-producing partially melted crushed ice,
-producing an ice repellent surface of the component,
-a refrigeration system for cooling the refrigerant,
-an air-conditioning system for conditioning air,
-producing an ice-cream, the ice-cream,
-avoiding the adhesion of ice on the surface of the components,
to avoid ice sticking on aircraft, helicopter wings, wind turbine blades or ships,
-avoiding the adhesion of limestone on the surface of the components,
-precipitation of the salt in the liquid,
-precipitation of calcium carbonate in a liquid,
-precipitation of magnesium carbonate in a liquid,
-precipitation of the sugar in the liquid,
-producing an ice slurry wherein a sub-cooled liquid stream is provided along the matrix to continuously remove precipitated ice from the nucleation sites;
-producing the material in a liquid under supersaturated conditions, wherein a flow of supersaturated liquid is provided along the substrate to continuously remove precipitated material from the nucleation sites;
-preventing the coated substrate from being covered by the substance in theliquid under supersaturated conditions, wherein a flow of supersaturated liquid is provided along the substrate to continuously remove precipitated substance from the nucleation sites; and
-preventing the coated substrate from being covered with ice in a water-containing fluid under supercooled conditions, comprising providing a flow of supercooled fluid along the substrate to continuously remove precipitated ice from the nucleation sites.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DKPA200100723 | 2001-05-08 | ||
| DKPA200100723 | 2001-05-08 |
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| CN1522288A CN1522288A (en) | 2004-08-18 |
| CN1283744C true CN1283744C (en) | 2006-11-08 |
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|---|---|---|---|
| CNB028133765A Expired - Fee Related CN1283744C (en) | 2001-05-08 | 2002-05-08 | Ice nucleating non-stick coating |
Country Status (8)
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| US (1) | US8371131B2 (en) |
| EP (1) | EP1392789B8 (en) |
| CN (1) | CN1283744C (en) |
| AT (1) | ATE463548T1 (en) |
| CA (1) | CA2447272C (en) |
| DE (1) | DE60235887D1 (en) |
| DK (1) | DK1392789T3 (en) |
| WO (1) | WO2002090459A1 (en) |
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| WO2005075112A1 (en) * | 2004-02-10 | 2005-08-18 | Multi Sign A/S | Surface coating with anti-dew and ice non-stick properties |
| WO2006034876A1 (en) * | 2004-09-30 | 2006-04-06 | Behr Gmbh & Co. Kg | Heat exchanger and a charge air cooling method |
| US7269967B2 (en) * | 2005-08-22 | 2007-09-18 | Gas Technology Institute | Method and apparatus for removing moisture from evaporator coils |
| DE102006060340B4 (en) | 2006-12-13 | 2012-12-13 | Leibniz-Institut Für Polymerforschung Dresden E.V. | Use of a durable coating of metal or glass surfaces to inhibit and / or prevent icing |
| FR2922522B1 (en) * | 2007-10-22 | 2010-04-16 | Aircelle Sa | PIEZOELECTRIC DEFROSTING OF AN AIR INPUT |
| US20110143148A1 (en) * | 2009-12-13 | 2011-06-16 | General Electric Company | Articles comprising a weather resistant silicone coating |
| US8844313B2 (en) | 2011-05-24 | 2014-09-30 | General Electric Company | Ice making assembly with bimetallic actuating element and refrigeration appliance incorporating same |
| DE102012208653B4 (en) | 2011-05-27 | 2019-04-25 | Technische Universität Bergakademie Freiberg | Process for the preparation of a surface coating with ice-repellent properties, surface coating and their use |
| US9964350B2 (en) | 2012-06-12 | 2018-05-08 | Hussmann Corporation | Control system for a refrigerated merchandiser |
| CA2787584A1 (en) | 2012-08-22 | 2014-02-22 | Hy-Power Nano Inc. | Method for continuous preparation of indium-tin coprecipitates and indium-tin-oxide nanopowders with substantially homogeneous indium/tin composition, controllable shape and particle size |
| US9199741B2 (en) * | 2014-03-07 | 2015-12-01 | The Boeing Company | Systems and methods for passive deicing |
| CN107787342A (en) | 2015-04-27 | 2018-03-09 | 密执安州立大学董事会 | Durability dredges ice surface |
| US10544974B2 (en) | 2017-09-01 | 2020-01-28 | Rebound Technologies, Inc. | Solid production methods, systems, and devices |
| US11965112B2 (en) | 2018-03-05 | 2024-04-23 | The Regents Of The University Of Michigan | Anti-icing surfaces exhibiting low interfacial toughness with ice |
| US11441830B2 (en) | 2018-12-26 | 2022-09-13 | Rebound Technologies, Inc. | Solid production systems, devices, and methods utilizing oleophilic surfaces |
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|---|---|---|---|---|
| US3272434A (en) * | 1963-06-03 | 1966-09-13 | Albert C Zettlemoyer | Nucleating process |
| US3858805A (en) * | 1973-10-31 | 1975-01-07 | Univ Lehigh | Ice nucleation by micas |
| US4484409A (en) * | 1982-03-29 | 1984-11-27 | University Patents, Inc. | Prevention of freezing at moderate supercooling using synthetic polymeric ice nucleation inhibitors |
| US5512329A (en) * | 1982-09-29 | 1996-04-30 | Bsi Corporation | Substrate surface preparation |
| US4585571A (en) * | 1985-03-15 | 1986-04-29 | Michael A. Bloom | Deicing compositions |
| DE3541100A1 (en) * | 1985-11-21 | 1987-05-27 | Bayer Ag | USE OF SILICONE MATERIALS TO PREVENT ICING ON SUBSTRATES |
| US4846886A (en) * | 1988-05-05 | 1989-07-11 | Dow Corning Corporation | Water beading-water shedding repellent composition |
| CA2017090A1 (en) * | 1990-05-17 | 1991-11-17 | Stephen Dunn | Coating composition |
| US5413865A (en) * | 1992-01-31 | 1995-05-09 | Central Glass Company, Limited | Water-repellent metal oxide film and method of forming same on glass substrate |
| US5736249A (en) * | 1994-08-16 | 1998-04-07 | Decora, Incorporated | Non-stick polymer-coated articles of manufacture |
| EP0716338B1 (en) * | 1994-12-09 | 2001-10-04 | Fuji Photo Film Co., Ltd. | Fine polymer particles having heterogeneous phase structure, silver halide photographic light- sensitive material containing the fine polymer particles and image-forming method |
| US5741828A (en) * | 1995-05-01 | 1998-04-21 | S.K.Y. Polymers, Inc. | Flexible hydrophilic composite coatings |
| DE19626162A1 (en) * | 1995-08-16 | 1998-01-08 | Johann Memmen | More effective waterproofing agent for use in building materials |
| AU6380999A (en) * | 1998-07-28 | 2000-02-21 | Arcelik A.S. | A method for preventing water accumulation and ice formation on the evaporators and condensers of refrigerators |
| JP4083323B2 (en) * | 1998-10-29 | 2008-04-30 | 東レ・ダウコーニング株式会社 | Method for producing organosilicon compound emulsion |
| JP3848527B2 (en) * | 2000-09-14 | 2006-11-22 | 積水樹脂株式会社 | Snow-ice ice coating |
| JP2002292410A (en) | 2001-03-29 | 2002-10-08 | Kawasaki Steel Corp | Removing method for joined protruding portion of hot- rolled blooms |
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- 2002-05-08 WO PCT/DK2002/000306 patent/WO2002090459A1/en not_active Application Discontinuation
- 2002-05-08 EP EP02742823A patent/EP1392789B8/en not_active Expired - Lifetime
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- 2002-05-08 DK DK02742823.4T patent/DK1392789T3/en active
- 2002-05-08 AT AT02742823T patent/ATE463548T1/en not_active IP Right Cessation
- 2002-05-08 CN CNB028133765A patent/CN1283744C/en not_active Expired - Fee Related
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| US20040249222A1 (en) | 2004-12-09 |
| EP1392789A1 (en) | 2004-03-03 |
| DE60235887D1 (en) | 2010-05-20 |
| CA2447272A1 (en) | 2002-11-14 |
| CA2447272C (en) | 2014-08-05 |
| CN1522288A (en) | 2004-08-18 |
| DK1392789T3 (en) | 2010-07-19 |
| EP1392789B1 (en) | 2010-04-07 |
| WO2002090459A1 (en) | 2002-11-14 |
| ATE463548T1 (en) | 2010-04-15 |
| US8371131B2 (en) | 2013-02-12 |
| EP1392789B8 (en) | 2010-05-26 |
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